email headers do not show normal ip

Wienel asked:

I am learning about mail servers, since the mail I send is not received by Hotmail. So I’m comparing mail headers from different sources to find out what could be my problem. I now have a very basic question. In the email headers I normally see this part:

Received: from ([ip.ip.ip.ip])
by with ESMTP ….

However, in the mail I send, I do not see the correct ip adres, but a very long number/string separated by colons, like this:

Received: from ([3201:7c8:xxxx:2de:xxxx:4dc3:xxxx:bf40])
by with ESMTP ….

What does this mean? Why do I not see a normal ip address?


My answer:

That looks like it might be an IPv6 address, though it’s difficult to tell since you have mangled it.

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